The present invention relates to a transmission system for hybrid traction vehicles, in particular of the industrial and agricultural type, of the type comprising a torque convertor and an electric motor which can be selectively actuated as a motor and as a generator.
Recently, in the field of industrial and agricultural vehicles, there has also become widespread the use of hybrid propulsion systems in which a non-reversible endothermic motor, generally an internal combustion engine, is associated with a reversible motor, of the electrical type, which can operate both as a motor and as a generator.
Typically, industrial vehicles use a torque converter which is actuated by the endothermic motor which transmits the movement to the wheels by means of a gearbox. More specifically, the endothermic motor is connected to the pump of the torque converter while the transmission portion associated with the wheels is connected to the turbine.
The endothermic motor is further connected to a power take-off, referred to as the PTO, which allows power to be supplied to auxiliary accessories of the vehicle, such as, for example, agricultural equipment or a pump for actuating auxiliary hydraulic devices.
The need to provide for the use of the above-mentioned components makes it all the more complex to define the most suitable architecture to be used in the hybrid systems for industrial vehicles.
Furthermore, it must be taken into consideration that the characteristics of use of industrial vehicles are highly discontinuous and variable, with driving steps alternating with static operating steps, unlike road vehicles which have curves of use of the motor which are well codified.
Consequently, the solutions which use the electrical propulsion in series with the endothermic motor and which are widely used in road vehicles are also not found to be suitable for hybrid industrial vehicles because in this case it would be necessary to have a complete re-design of the transmission which is not justified by the numbers, which are currently generally still relatively modest, of hybrid industrial vehicles.
As an alternative to series type solutions, the patent application US 2009/0018716 discloses a hybrid vehicle which comprises an internal combustion engine which is connected by means of a driven wheel transmission, a power take-off (PTO) which is connected to the transmission and which is capable of supplying power to an accessory device, a hybrid traction system which is connected in parallel to the power take-off and which comprises an electric motor, an energy accumulation system and a system for monitoring and controlling the vehicle. The connection between the transmission and the hybrid traction system is constructed by connecting the electric motor to the force take-off by means of a shaft so as to produce a bi-directional flow of power.
In this manner, when acceleration is brought about, the system operates in such a mode as to provide electrical energy in order to supply power to the transmission, supplementing the motive power provided by the internal combustion engine, while in a deceleration step the electric motor acts as a generator in order to supply a regenerative braking in order to recharge an energy accumulation system.
In addition, the system may operate in a mode in which power is not provided for the wheels and in which the power take-off is disconnected from the transmission and the energy is supplied by the electric motor to the accessory device.
Although the parallel configuration described in that patent application does not require a complete re-design of the transmission with respect to the series type solutions, being suitable for retro-fitting of existing transmissions, it is not found to be optimal from the point of view of the efficiency and the spatial requirement.
Therefore, the technical problem addressed by the present invention is to provide a transmission for vehicles which allows the disadvantages mentioned above with reference to the prior art to be overcome.
That problem is solved by the transmission system according to the invention.